ERROR ITMS-90296: "App sandbox not enabled. The following executables must include the "com.apple.security.app-sandbox" entitlement with a Boolean value of true in the entitlements property list: [( "com.amit.CVLive.pkg/Payload/CvLive.app/Contents/MacOS/CvLive", "com.amit.CVLive.pkg/Payload/CvLive.app/Contents/Resources/FFMPE3/ffmpeg", "com.amit.CVLive.pkg/Payload/CvLive.app/Contents/Resources/ffmpeg" )] Refer to App Sandbox page at https://developer.apple.com/devcenter/mac/app-sandbox/ for more information onsandboxing your app."

Make sure you have enabled sandboxing on all Mach-O executables included in your application's bundle. Every Mach-O executable must have an entitlements file, and request the com.apple.security.app-sandbox entitlement. This includes XPC services and custom helper tools that request the com.apple.security.inherit entitlement. They must also request the com.apple.security.app-sandbox entitlement.

Did you read that ?

All component provided in you .app bundle should run in sandboxed mode.

So you need to compile ffmpeg on your own inside you project with sandboxed mode enabled. (dunno how to do this, refer to Apple dev doc)

Perhaps Apple provide support if you have a real developper account as it cost 100 $